The invention relates to a circuit arrangement for operating a solenoid actuator, and more particularly, a circuit arrangement in which an energy feed-back device is located between an energy supply device and the actuator for feeding back an energy quantity stored in the actuator into the energy supply -device to provide supplementary operating power as needed.
A circuit arrangement of this type is disclosed, for example, in U.S. Pat. No. 5,432,420 issued to Bahn. The disclosed circuit arrangement operates a solenoid actuator provided in the form of an electric motor, in particular, a switched reluctance motor or a brushless D.C. motor. Motors of this type are provided with a stator having several exciter windings, and a rotor located therein made of a magnetic material, or one which can be magnetized. By feeding electric current sequentially to the exciter winding, a rotary field is created inside the stator which causes the rotor to rotate. In order to attain a rotational speed of the rotor suitable for practical use, the exciter windings must be subjected to current at relatively brief time intervals. Since the inductive behavior of the exciter winding causes a relatively slow rise in current at first, and then a relatively slow drop in current, without additional measures being taken, the operation of motors of this type is relatively inefficient.
In order to achieve efficient operation, each exciter winding of the electric motor is connected to a capacitor which serves as an energy storage in the above-mentioned circuit arrangement. When the exciter winding is switched off, two diodes cause a pole-dependent feed-back of the energy stored in the exciter winding, in the form of a current, into the corresponding capacitor, so that increased voltage is built up therein as compared with the nominal operating voltage of the circuit arrangement. In the next actuating step of the electric motor, this energy, which is stored in the capacitor, is transferred to the next exciter winding which is to be subjected to voltage, in order to improve the effectiveness of the electric motor.
In the power supply of solenoid actuators, such as, an electric motor or a valve actuated by an electric motor, a battery used to provide the power may have a defect, for example, a short circuit between the electrodes of the battery, resulting in a reduction in available voltage. It is also possible that the battery may fail completely. For such instances, and in particular with regard to safety-relevant systems, such as those used in a vehicle, an auxiliary battery may be provided. For economic reasons, a relatively small battery with a relatively low nominal voltage is preferably used as the auxiliary battery.
In such cases, however, because of the reduced operating voltage, the solenoid actuator may produce an insufficient actuating force for the situation for which it is intended. This could have far-reaching and undesirable consequences in a safety-relevant system.
It is therefore an object of the present invention to provide a circuit arrangement for the operation of a solenoid actuator capable of producing sufficient actuating force to ensure safe operation even in the event of an insufficient power supply to the actuator.
In accordance with this and other objects of the invention, there is provided a circuit arrangement for operating a solenoid actuator which includes an electrical energy supply device and a first switching device via which the actuator is connectable to the electrical energy supply device. An energy feed-back device is provided between the energy supply device and the actuator for feeding back an energy quantity stored in the actuator into the energy supply device when the first switching device is opened. The energy supply device includes at least one energy output device and at least one energy storage for transmitting and receiving energy. A second switching device is also provided, via which the energy storage is connectable to the energy feed-back device, such that a desired energy reserve is accumulated step by step in the energy storage by an alternating opening and closing of the first and the second switching devices.
The invention provides the advantage that, in comparison with the state of the art, no additional components, such as a separate inductor, are required. As a result, the invention can be implemented very economically. In particular, no additional inductance device or coil is required to collect the energy reserve in the energy storage, such as is required, for example, in a circuit regulator according to known voltage supply technology, since the inductance of one or several exciter windings of the solenoid actuator is utilized directly in accordance with the invention.
In order to accumulate a desired energy reserve in the energy storage, only an alternating opening and closing of the first and second switching devices is required. The desired energy reserve can be built up by means of the number of opening and closing cycles, depending on the application, and can later be transferred to the actuator to increase the actuating force. Depending upon the storage capacity of the energy storage and of the actuator, and depending upon the operating voltage of the energy supply system, a greater or lesser number of opening and closing cycles may be required. This must be adapted as a function of each particular special application.
The invention provides the further advantage that even when an operating voltage is much lower than the normal operating voltage, it is still possible to operate the actuator, and the actuator is still able to function as long as any operating voltage is still present. As a result, an especially high degree of operating safety is achieved.
When applying the invention in combination with an energy supply system with several batteries used as energy supply devices, for example, a main battery serving as main energy supply device and an auxiliary battery provided as a redundancy, it is also possible to use a relatively small battery as compared with the main battery with considerably less voltage, so that the energy supply system can be produced at relatively low cost.
Furthermore the invention can also be used advantageously for the temporary increase of the actuating force of the actuator, for example, when a greater actuating force is needed for a short period of time than can be attained by the operation of the actuator with the normal operating voltage of the energy supply system.
In an advantageous embodiment of the invention, the first switching system is actuated in such manner in the energy storage mode that the actuator essentially executes no actuating movement. Depending upon the actuator, this can also be achieved, for example, through a relatively short actuation of the first switching device or, in case of actuators of a different type, also by switching on one or several very specific exciter windings of the actuator for a longer period of time as required.
If, for example, a switched reluctance motor is used as the actuator, the first switching means can be actuated preferably in such manner that the exciter winding of the reluctance motor with stator poles closest to the rotor poles is connected to the energy supply system. In such case, the reluctance motor does not execute any substantial movement. It is an additional advantage, in this case, that the previously mentioned exciter winding has the highest inductance of all exciter windings of the reluctance motor due to the position of the rotor, so that the accumulation of the energy reserve in the energy storage can take place at a relatively high speed.
Depending on the design of the reluctance motor, or of some other electric motor, it may also be advantageous to connect several or all exciter windings at the same time to the energy supply system, such that when the first switching means has been opened, the energy quantities from several or all exciter windings is stored in the energy storage, so that the accumulation of the energy reserve in the energy storage is thus accelerated further.
It is another advantage of the invention that when an electric motor with several exciter windings is used, only a single energy storage, for example, a capacitor, is required. For this reason, the invention can be particularly economical in its implementation.